Display and labeled article

ABSTRACT

A display includes one or more first relief structures. Each of the one or more first relief structures consists of a smooth first reflection surface and a plurality of protrusions or recesses, each top surface of the protrusions or each bottom of the recesses is a smooth second reflection surface parallel to the first reflection surface, each of the one or more first relief structures is configured to display a color as a structural color by emitting a plurality of wavelength components of visible light wavelengths in the same direction, and each of the second reflection surfaces has a height or depth relative to the first reflection surface in a range of 0.1 to 0.5 μm.

CROSS REFERENCE TO RELATED APPLICATIONS

This is a continuation application of U.S. application Ser. No.13/485,284 filed May 31, 2012, which is a Continuation Application ofPCT Application No. PCT/JP2010/069313, filed Oct. 29, 2010 and basedupon and claiming the benefit of priority from prior Japanese PatentApplications No. 2009-273406, filed Dec. 1, 2009; No. 2010-023976, filedFeb. 5, 2010; No. 2010-074744, filed Mar. 29, 2010; and No. 2010-089381,filed Apr. 8, 2010, the entire contents of all of which are incorporatedherein by reference.

BACKGROUND 1. Field

The present invention relates to a display technique that offers, forexample, a forgery-prevention effect.

2. Description of Related Art

Generally, in order to prevent forgery of securities such as vouchersand checks, cards such as credit cards, cash cards, and ID cards, andcertificates such as passports and driver's licenses, theses articlesare provided with a display that offers a visual effect different fromthat offered by a common printed matter. In recent years, for otherarticles in addition to the above-described articles, distribution offorged articles has become an issue of social concern. Thus,opportunities to apply similar forgery-prevention technique to sucharticles are increasing.

A display including an arrangement of grooves as a diffraction gratingis known as one of displays offering a visual effect different from thatoffered by a common printed matter. The display can be formed todisplay, for example, an image that changes in accordance withobservation conditions or a stereoscopic image. Iridescent spectralcolors displayed by the diffraction grating cannot be created by commonprinting techniques. Thus, a display including a diffraction grating iswidely used for articles requiring forgery-prevention measures.

Jpn. Pat. Appln. KOKAI Publication No. 2-72320 describes arrangingdiffraction gratings different from each other in the lengthwisedirections of the grooves or grating constants, i.e., pitches ofgrooves, so as to display a pattern. When the position of an observer orlight source relative to the diffraction grating changes, the wavelengthof diffracted light reaching eyes of the observer changes. Therefore, ifthe above configuration is adopted, an image changing iridescently canbe displayed.

A display using a diffraction grating generally uses a relief-typediffraction grating. A relief-type diffraction grating is normallyobtained by duplicating a pattern of a master produced usingphotolithography.

U.S. Pat. No. 5,058,992 describes a method of manufacturing a masterhaving a relief-type diffraction grating thereon in which a plate-shapedsubstrate having a photosensitive resist applied thereon is placed on anXY stage, and the photosensitive resist is irradiated with an electronbeam while moving the stage under the control of a computer so as toperform pattern exposure on the photosensitive resist. A master having adiffraction grating can also be formed by using two-beam interference.

In the production of a relief-type diffraction grating, first, a masteris normally formed by one of methods as described above and then ametallic stamper is produced by, for example, an electroformingtechnique using the master. Next, the metallic stamper is used as amother die to duplicate the relief-type diffraction grating. That is,first, a thermoplastic resin or photo-curable resin is applied to afilm- or sheet-shaped thin transparent substrate made of, for example,polyethylene terephthalate (PET) or polycarbonate (PC). Next, a metallicstamper is brought into close contact with the coated film and heat orlight is applied to the resin layer in this state. After curing theresin, the metallic stamper is removed from the cured resin so as toobtain a duplicate relief-type diffraction grating.

Generally, the relief-type diffraction grating is transparent. Thus, areflection layer is normally formed on the resin provided with therelief structure by depositing a single layer or a plurality of layersof a metal such as aluminum or a dielectric by using the evaporationmethod.

Subsequently, the display obtained as described above is pasted on asubstrate made of, for example, paper or a plastic film via an adhesivelayer or sticky layer. Thus, the display adopting forgery-preventionmeasures is obtained.

The master used for producing the display including the relief-typediffraction grating is difficult to manufacture. Moreover, a reliefstructure needs to be transferred from the metallic stamper to the resinlayer with high precision. That is, a high level of technique isrequired to produce a display including a relief-type diffractiongrating.

However, as a result of the fact that the display including arelief-type diffraction grating is increasingly used in many articlesrequiring forgery-prevention measures, the technique is now widelyrecognized and accordingly, forgeries tend to increase. Thus, it isbecoming increasingly more difficult to achieve a sufficientforgery-prevention effect by using a display only featured in thatiridescent light is presented by diffracted light.

BRIEF SUMMARY

An object of the present invention is to provide a display offeringcharacteristic visual effects.

According to a first aspect of the present invention, there is provideda display including one or more first relief structures, wherein each ofthe one or more first relief structures includes a smooth firstreflection surface and a plurality of protrusions or recesses, each topsurface of the protrusions or each bottom of the recesses is a smoothsecond reflection surface parallel to the first reflection surface, andeach of the one or more first relief structures is configured to displaya mixed color as a structural color by mixing a plurality of wavelengthcomponents of visible light wavelengths.

According to a second aspect of the present invention, there is provideda labeled article comprising the display according to the first aspect,and an article supporting the display.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

FIG. 1 is a plan view schematically showing a display according to thefirst embodiment of the present invention;

FIG. 2 is a sectional view taken along an II-II line of the displayshown in FIG. 1;

FIG. 3 is a diagram schematically showing a situation in which adiffraction grating having a small grating constant emits first-orderdiffracted light;

FIG. 4 is a diagram schematically showing a situation in which adiffraction grating having a large grating constant emits first-orderdiffracted light;

FIG. 5 is a plan view schematically showing an example of a first reliefstructure that can be adopted for the display shown in FIG. 1;

FIG. 6 is a sectional view taken along a VI-VI line of the structureshown in FIG. 5;

FIG. 7 is a plan view schematically showing another example of the firstrelief structure that can be adopted for the display shown in FIG. 1;

FIG. 8 is a plan view schematically showing another example of the firstrelief structure that can be adopted for the display shown in FIG. 1;

FIG. 9 is a plan view schematically showing another example of the firstrelief structure that can be adopted for the display shown in FIG. 1;

FIG. 10 is a plan view schematically showing another example of thefirst relief structure that can be adopted for the display shown in FIG.1;

FIG. 11 is a plan view schematically showing another example of thefirst relief structure that can be adopted for the display shown in FIG.1;

FIG. 12 is a diagram schematically showing the situation in which adiffraction grating emits diffracted light;

FIG. 13 is a diagram schematically showing the situation in which afirst relief structure emits scattered light;

FIG. 14 is a plan view schematically showing still another example ofthe first relief structure that can be adopted for the display shown inFIG. 1;

FIG. 15 is a diagram schematically showing the situation in which thefirst relief structure having the second reflection surfaces irregularlyarranged displays a mixed color as a structural color;

FIG. 16 is a diagram schematically showing the situation in which lightsreflected by the first and second reflection surfaces interfere witheach other;

FIG. 17 is a u′v′ chromaticity diagram showing an example of colorchanges caused when the difference between the heights of the first andsecond reflection surfaces is changed in the range of 0.10 to 0.30 μm;

FIG. 18 is a u′v′ chromaticity diagram showing an example of colorchanges caused when the difference between the heights of the first andsecond reflection surfaces is changed in the range of 0.30 to 0.50 μm;

FIG. 19 is a u′v′ chromaticity diagram showing an example of colorchanges caused when the difference between the heights of the first andsecond reflection surfaces is changed in the range of 0.50 to 0.70 μm;

FIG. 20 is a u′v′ chromaticity diagram showing an example of colorchanges caused when the angle of incidence θ₀ of illumination light iscontinuously changed in the range of 0° to 90°;

FIG. 21 is a u′v′ chromaticity diagram showing an example of colorchanges caused when the angle of incidence θ₀ of illumination light iscontinuously changed in the range of 20° to 40°;

FIG. 22 is a sectional view schematically showing an example of thediffraction grating;

FIG. 23 is a sectional view schematically showing another example of thediffraction grating;

FIG. 24 is a perspective view schematically showing an example of thestructure that can be adopted for the second relief structure;

FIG. 25 is a perspective view schematically showing another example ofthe structure that can be adopted for the second relief structure;

FIG. 26 is a plan view schematically showing an example of the structurethat can be adopted for a display according to the second embodiment ofthe present invention;

FIG. 27 is an enlarged plan view showing a portion of the structureshown in FIG. 26;

FIG. 28 is a sectional view taken along an XXI-XXI line of the structureshown in FIG. 26;

FIG. 29 is a plan view schematically showing an example of thearrangement of pixels;

FIG. 30 is a plan view schematically showing another example of thearrangement of pixels;

FIG. 31 is a diagram schematically showing examples of images that canbe displayed by the display according to the second embodiment of thepresent invention;

FIG. 32 is a sectional diagram schematically showing an example of thestructure that can be adopted for a display according to the thirdembodiment of the present invention;

FIG. 33 is a sectional diagram schematically showing another example ofthe structure that can be adopted for a display according to the thirdembodiment of the present invention;

FIG. 34 is a sectional diagram schematically showing still anotherexample of the structure that can be adopted for a display according tothe third embodiment of the present invention;

FIG. 35 is a plan view schematically showing an example of the imagedisplayed by the display according to the third embodiment of thepresent invention when an observer observes it from the normaldirection;

FIG. 36 is a perspective view schematically showing an example of theimage displayed by the display shown in FIG. 35 when an observerobserves it from an oblique direction;

FIG. 37 is a plan view schematically showing another example of theimage displayed by the display according to the third embodiment of thepresent invention when an observer observes it from the normaldirection;

FIG. 38 is a perspective view schematically showing an example of theimage displayed by the display shown in FIG. 37 when an observerobserves it from an oblique direction;

FIG. 39 is a plan view schematically showing a modification of thedisplay shown in FIG. 33;

FIG. 40 is a sectional view taken along an XXXIII-XXXIII line of thedisplay shown in FIG. 39;

FIG. 41 is a perspective view schematically showing an example of theimage displayed by the display shown in FIGS. 39 and 40 when an observerobserves it from the oblique direction;

FIG. 42 is a perspective view schematically showing an example of thestructure that can be adopted for a display according to the fourthembodiment of the present invention;

FIG. 43 is a plan view schematically showing an example of amodification of the relief structure shown in FIG. 42;

FIG. 44 is a plan view schematically showing another example of themodification of the relief structure shown in FIG. 42;

FIG. 45 is a plan view schematically showing an example of the displayincluding the relief structure shown in FIG. 42;

FIG. 46 is a perspective view schematically showing an example of theimage displayed by the display shown in FIG. 45;

FIG. 47 is a perspective view schematically showing another example ofthe image displayed by the display shown in FIG. 45;

FIG. 48 is a plan view schematically showing an example of a labeledarticle; and

FIG. 49 is a sectional view taken along an IL-IL line of the labeledarticle shown in FIG. 48.

DETAILED DESCRIPTION

Embodiments of the present invention will be hereinafter described indetail with reference to drawings. It should be noted that constituentelements achieving the same or similar functions are denoted with thesame reference numerals throughout the drawings, and redundantexplanation thereof is omitted.

First Embodiment

First, the first embodiment of the present invention will be described.

FIG. 1 is a plan view schematically showing a display according to thefirst embodiment of the present invention. FIG. 2 is a sectional viewtaken along an II-II line of the display shown in FIG. 1. In FIGS. 1 and2, the X direction and the Y direction are directions parallel to adisplay surface and perpendicular to each other. The Z direction is adirection perpendicular to the X direction and the Y direction.

As shown in FIG. 2, a display 1 includes a layered product of alight-transmitting layer 11 and a reflection layer 12. In this example,the side on the light-transmitting layer 11 is assumed to be a frontside, i.e., observer's side and the side on the reflection layer 12 isassumed to be a back side.

The light-transmitting layer 11 includes a substrate 111 and a reliefstructure formation layer 112.

The substrate 111 has light-transmitting properties. The substrate 111is typically transparent and particularly transparent and colorless. Asthe material of the substrate 111, for example, a resin havingrelatively high heat resistance such as PET and polycarbonate (PC) canbe used.

The substrate 111 is a film or sheet that can be handled alone. Thesubstrate 111 plays a role as an underlayer of the relief structureformation layer 112 and also plays a role in protecting the reliefstructure formation layer 112 from damage. The substrate 111 can beomitted.

The relief structure formation layer 112 is a layer formed on thesubstrate 111. The relief structure formation layer 112 haslight-transmitting properties. The relief structure formation layer 112is typically transparent and particularly transparent and colorless.

The portion of the surface of the relief structure formation layer 112that is positioned inside the region 13 shown in FIG. 1 and the portionof the surface of the relief structure formation layer 112 that ispositioned inside the region 17 shown in FIG. 1 are provided with afirst relief structure RS1 and a second relief structure RS2, which aredescribed later, respectively. The portion of the surface of the reliefstructure formation layer 112 that is positioned inside the region 18 isflat.

As the material of the relief structure formation layer 112, forexample, a thermoplastic resin or photo-curable resin can be used. Therelief structure formation layer 112 can be obtained by, for example,applying the thermoplastic resin or photo-curable resin onto thesubstrate 111 and setting the resin while pressing a stamper against theapplied film.

The reflection layer 12 covers a surface of the relief structureformation layer 112 on which the relief structures RS1 and RS2 areprovided. As the reflection layer 12, for example, a metal layer made ofa metallic material such as aluminum, silver, gold, or an alloy thereofcan be used. Alternatively, as the reflection layer 12, a dielectriclayer having a refractive index different from that of the reliefstructure formation layer 112 may be used. In addition, as thereflection layer 12, a layered product of dielectric layers in whichadjacent dielectric layers have different refractive indexes, that is, adielectric multilayer film may also be used. Incidentally, therefractive index of, among dielectric layers contained in the dielectricmultilayer film, the dielectric layer in contact with the reliefstructure formation layer 112 is desirably different from that of therelief structure formation layer 112. The reflection layer 12 can beformed by, for example, the vapor phase deposition method such as vacuumevaporation method and sputtering method.

The reflection layer 12 may cover the entire surface on which the reliefstructures RS1 and RS2 are provided or a portion thereof. The reflectionlayer 12 covering only a portion of the relief structure formation layer112, that is, the patterned reflection layer 12 is obtained by, forexample, forming a reflection layer as a continuous film by the vaporphase deposition method and then dissolving a portion thereof with achemical or the like. Alternatively, the patterned reflection layer 12is obtained by forming a reflection layer as a continuous film and thenpeeling off a portion of the reflection layer from a relief structureformation layer by using an adhesive material whose adhesive strength tothe reflection layer is stronger than that of the reflection layer tothe relief structure formation layer. Alternatively, the patternedreflection layer 12 is obtained by performing vapor phase depositionusing a mask or using a lift-off process.

The display 1 may further contain other layers such as an adhesivelayer, a resin layer, and a print layer.

The adhesive layer is provided, for example, to cover the reflectionlayer 12. When the display 1 contains both the light-transmitting layer11 and the reflection layer 12, normally the shape of the surface of thereflection layer 12 is approximately the same as that of an interfacebetween the light-transmitting layer 11 and the reflection layer 12.When an adhesive layer is provided, the surface of the reflection layer12 can be prevented from being exposed, making duplication for thepurpose of forging the relief structure in the above interface moredifficult. When the side on the light-transmitting layer 11 is set asthe back side and the side on the reflection layer 12 is set as thefront side, an adhesive layer is formed on the light-transmitting layer11.

The resin layer is, for example, a hard coating for preventing thesurface of the display 1 from being scratched in use, an antifoulinglayer to limit adhesion of dirt, an antireflection layer to preventreflection of light on a substrate surface, or an antistatic layer. Theresin layer is provided on the front side of a layered product of thelight-transmitting layer 11 and the reflection layer 12. If, forexample, the side on the light-transmitting layer 11 is the back sideand the side on the reflection layer 12 is the front side, in additionto being able to limit damage to the reflection layer 12 by covering thereflection layer 12 with a resin layer, duplication for the purpose offorging the relief structure on the surface thereof can be made moredifficult.

Next, the relief structures RS1, RS2 will be described.

In the display 1 shown in FIGS. 1 and 2, the relief structures RS1 andRS2 are provided on the surface of the reflection layer 12.

The relief structure RS1 is provided on the surface of the reliefstructure formation layer 112 at a position corresponding to the region13 shown in FIG. 1. Here, three relief structures RS1 are provided onthe surface of the relief structure formation layer 112 and these reliefstructures RS1 display letters “T”, “O”, and “P” shown in FIG. 1.

The relief structure RS2 is provided on the surface of the reliefstructure formation layer 112 at a position corresponding to the region17 shown in FIG. 1. These relief structures RS2 display shadows of theletters “T”, “O”, and “P” displayed by the relief structures RS1.

The relief structures RS1 and RS2 have different structures, as will bedescribed below.

(First Relief Structure)

Before describing the first relief structure RS1, a relationship betweena grating constant of a diffraction grating, i.e., groove pitch, awavelength of illumination light, an angle of incidence of illuminationlight, and an angle of emergence of diffracted light will be described.

When a diffraction grating is irradiated with illumination light byusing an illumination light source, the diffraction grating emits strongdiffracted light in a specific direction in accordance with thetraveling direction and the wavelength of the illumination light, whichis incident light.

When light travels in a plane perpendicular to the length direction ofthe grooves of the diffraction grating, an angle of emergence β ofmth-order diffracted light (m=0, ±1, ±2, . . . ) can be calculated fromthe following equation (1).

$\begin{matrix}{d = \frac{m\; \lambda}{{\sin \; \alpha} - {\sin \; \beta}}} & (1)\end{matrix}$

In the equation (1), d denotes the grating constant of the diffractiongrating, m denotes the diffraction order, and λ denotes the wavelengthof incident light and diffracted light. α denotes the 0-orderdiffraction, that is, the angle of emergence of regular reflection lightRL. In other words, the absolute value of α is equal to the angle ofincidence of illumination light and in the case of a reflection grating,the direction of incidence of illumination light and the direction ofemergence of regular reflection light are symmetrical with respect to anormal NL of an interface where the diffraction grating is provided.

Note that in the case where the diffraction grating is of reflectiontype, the angle α is 0° or more and less than 90°. Note also that in thecase where illumination light is radiated in an oblique direction withrespect to the interface having the diffraction grating provided thereonand two ranges of angle separated by a boundary value of the angle in anormal direction, that is, 0° are considered, the angle β is a positivevalue when the direction of emergence of diffracted light and thedirection of emergence of regular reflection light are in the same rangeof angle and the angle β is a negative value when the direction ofemergence of diffracted light and the direction of incidence ofillumination light are in the same range of angle.

FIG. 3 is a diagram schematically showing a situation in which adiffraction grating having a small grating constant emits first-orderdiffracted light. FIG. 4 is a diagram schematically showing a situationin which a diffraction grating having a large grating constant emitsfirst-order diffracted light.

A point light source LS radiates white light including a light componentR whose wavelength is in a red region, a light component G whosewavelength is in a green region, and a light component B whosewavelength is in a blue region. The light components G, B and R emittedby the point light source LS are incident on a diffraction grating GR atthe angle of incidence α. The diffraction grating GR emits diffractedlight DL_g as a portion of the light component G at an angle ofemergence β_g, diffracted light DL_b as a portion of the light componentB at an angle of emergence β_b, and diffracted light DL_r as a portionof the light component R at an angle of emergence β_r. Though notillustrated, the diffraction grating GR also emits diffracted lights ofother orders at angles derived from the equation (1).

Thus, under fixed illumination conditions, the diffraction grating emitsdiffracted light at different angle in accordance with the wavelengththereof. Accordingly, the diffraction grating emits lights of differentwavelengths at different angles under a white light source such as thesun and a fluorescent lamp. Therefore, under such illuminationconditions, the display color iridescently changes with changes of theobservation angle. With an increasing grating constant, diffracted lightis emitted in a direction closer to that of the regular reflection lightRL, making differences of the angles of emergence β_g, β_b and β_rsmaller.

Next, the relationship between the grating constant of a diffractiongrating, the wavelength of illumination light, and intensity ordiffraction efficiency of diffracted light in a direction of the angleof emergence of the diffracted light will be described.

According to the equation (1), if illumination light is incident on adiffraction grating of the grating constant d at the angle of incidenceα, the diffraction grating emits diffracted light at the angle ofemergence β. In this case, the diffraction efficiency of light of thewavelength λ changes in accordance with the grating constant and groovedepth and the like of the diffraction grating and can be calculated fromthe equation (2).

$\begin{matrix}{\eta = {( \frac{2}{\pi} )^{2} \times {\sin^{2}( {\frac{2\; \pi}{\lambda} \times \frac{r}{\cos \; \theta}} )} \times {\sin^{2}( {\frac{\pi}{d} \times L} )}}} & (2)\end{matrix}$

In the equation, η denotes the diffraction efficiency (value from 0 to1), r denotes the groove depth of the diffraction grating, L denotes thegroove width of the diffraction grating, d denotes the grating constant,θ denotes the angle of incidence of illumination light, and λ denotesthe wavelength of illumination light and diffracted light. The equation(2) applies only to a diffraction grating in which the sectionperpendicular to the direction of groove length has a rectangular waveshape and the groove is relatively shallow.

As is evident from the equation (2), the diffraction efficiency ηchanges in accordance with the groove depth r, the grating constant d,the angle of incidence θ, and the wavelength λ. In addition, thediffraction efficiency η tends to gradually decrease with an increasingdiffraction order m.

Next, the structure and optical properties of the relief structure RS1will be described.

FIG. 5 is a plan view schematically showing an example of a first reliefstructure that can be adopted for the display shown in FIG. 1. FIG. 6 isa sectional view taken along a VI-VI line of the structure shown in FIG.5.

The relief structure RS1 includes a smooth first reflection surface 21and a plurality of protrusions each having a top surface and a sidesurface or a plurality of recesses each having a bottom and a sidesurface. The top surface of the protrusion or the bottom of the recessis a smooth second reflection surface 22 parallel to the firstreflection surface 21. It is assumed here as an example that the secondreflection surface 22 constitutes the top surface of a protrusion whenviewed from the side on the substrate 111.

The protrusion or recess has a circular shape when viewed from adirection perpendicular to the reflection surface 21. The protrusions orrecesses are arranged regularly. In this example, the arrangement of theprotrusions or recesses forms a triangular lattice. The arrangement ofthe protrusions or recesses may also form other lattices, for example, asquare lattice or rectangular lattice. When such arrangements areadopted, diffracted light originating from a periodical structure of thediffraction grating can be used for the display.

The reflection surfaces 22 have the same shape and dimensions. Thereflection surfaces 22 have a circular shape in this example. Thereflection surfaces 22 are arranged regularly corresponding to theprotrusions or recesses.

The reflection surface 22 has the length and width in the range of, forexample, 2 to 50 μm, 5 to 50 μm, or 0.3 to 10 μm. The reflectionsurfaces 22 are arranged at average intervals in the range of, forexample, 2 to 50 μm, 5 to 50 μm, or 0.3 to 10 μm. When thecenter-to-center distance of the reflection surfaces 22 is sufficientlylong, the angle of emergence of diffracted light can be restricted to anarrow range of angle. That is, diffracted lights of differentwavelengths can be made to be incident on eyes of an observer at thesame time and therefore, the observer can made to perceive a mixedcolor. However, if the center-to-center distance of the reflectionsurfaces 22 is too long, it becomes more difficult to cause the reliefstructure RS1 to emit diffracted light of sufficient intensity.

The length and width of the reflection surface 22 are measured as shownbelow. First, among line segments each connecting two points on acontour of the reflection surface 22, the line segment with the maximumlength from is determined. The length of the line segment is set as thelength of the reflection surface 22. Next, among rectangles and squareshaving sides parallel to the line segment and circumscribing the contourof the reflection surface 22, a rectangle or a square with the minimumarea is selected. The width of the reflection surface 22 is the lengthof sides of the rectangle and square perpendicular to the line segment.

The height of the reflection surface 22 relative to the reflectionsurface 21 is, for example, in the range of 0.1 to 0.5 μm and typically,in the range of 0.15 to 0.4 μm. The height of the reflection surface 22relative to the reflection surface 21 affects diffraction efficiency.When the height is in the above range, a bright display becomespossible. When the height is decreased, the influence of slight changesof external factors during production, for example, the state ofmanufacturing equipment, variations of the environment, and materialcomposition on optical properties of the relief structure RS1 increases.On the other hand, when the height is increased, it becomes difficult toform the relief structure RS1 with high precision in shape anddimension.

If the above height is set appropriately, when the relief structure RS1is illuminated with white light from a specific direction, a firstreflected light having a wavelength in the visible region and reflectedby the reflection surface 21 and a second reflected light having thewavelength and reflected by the reflection surface 22 may causeconstructive interference or destructive interference. When the reliefstructure RS1 is formed with high precision in shape, the reliefstructure RS1 can be caused to emit colored light as reflected light byusing the constructive interference or destructive interference.

In each of the relief structures RS1, all the reflection surfaces 22contained therein may have a fixed height relative to the reflectionsurface 21 or have different heights.

Typically, in each of the relief structures RS1, all the reflectionsurfaces 22 contained therein have a fixed height relative to thereflection surface 21. Such a structure is advantageous to make thediffraction efficiency in some wavelength band lower than that in otherwavelength bands.

The side surface of a protrusion (the side wall for a recess) extendingfrom an edge of the reflection surface 21 to an edge of the reflectionsurface 22 is nearly perpendicular to the reflection surface 21. Theside wall (or the side surface) may be inclined to the reflectionsurface 21.

When the area of an orthogonal projection of the relief structures RS1on a plane parallel to the reflection surface 21 is S, a ratio S1/S ofan area S1 of the reflection surface 21 to the area S is, for example,in the range of 20% to 80% and typically, in the range of 40% to 60%. Aratio S2/S of an area S2 of the reflection surface 22 to the area S is,for example, in the range of 80% to 20% and typically, in the range of60% to 40%. Also, a ratio (S1+S2)/S of the sum of the area S1 and thearea S2 to the area S is, for example, 10% to 100% and typically, in therange of 50% to 100%. When the ratios S1/S and S2/S are 50% each, thebrightest display becomes possible. According to an example, thebrightness that can be achieved when one of the ratios S1/S and S2/S is20% and the other is 80% is about 30% of the brightness that can beachieved when the ratios S1/S and S2/S are 50% each.

FIGS. 7 to 11 are plan views schematically showing other examples of thefirst relief structure that can be adopted for the display shown in FIG.1.

The relief structures RS1 shown in FIGS. 7 to 11 are similar to therelief structure RS1 shown in FIGS. 5 and 6 excluding the followingpoints.

That is, the reflection surface 22 has an elliptic shape in the reliefstructure RS1 shown in FIG. 7. The reflection surface 22 has anoctagonal shape in the relief structure RS1 shown in FIG. 8. Thereflection surface 22 has a star shape and is arranged irregularly inthe relief structure RS1 shown in FIG. 9. The reflection surface 22 hasa cross shape and is arranged irregularly in the relief structure RS1shown in FIG. 10. The reflection surface 22 has a square shape and isarranged irregularly in the relief structure RS1 shown in FIG. 11. InFIG. 11, some of the adjacent reflection surfaces 22 are in contact witheach other. In FIG. 7, L and W denote the length and width of thereflection surface 22, respectively. As above, the reflection surface 22can have various shapes. As will be described later, the reflectionsurface 22 may be arranged regularly or irregularly. When the reflectionsurface 22 is arranged irregularly, the adjacent reflection surfaces 22may be in contact with each other.

FIG. 12 is a diagram schematically showing the situation in which adiffraction grating emits diffracted light. FIG. 13 is a diagramschematically showing the situation in which a first relief structureemits scattered light.

The diffraction grating in FIG. 12 is composed of a plurality of groovesGR having the length direction parallel to the Y direction and arrangedin the X direction with a fixed pitch. When illumination light IL isincident on the relief structure RS1 in a direction perpendicular to theY direction, for example, the Z direction, the diffraction grating emitsdiffracted lights DL_r, DL_g and DL_b in a direction perpendicular tothe Y direction. Each angle of emergence of the diffracted lights DL_r,DL_g and DL_b is calculated from the equation (1).

In the relief structure RS1 shown in FIG. 13, the reflection surfaces 22are arranged two-dimensionally. Thus, when the illumination light IL isincident on the relief structure RS1 from, for example, the Z direction,the relief structure RS1 emits the diffracted lights DL_r, DL_g and DL_bin various directions.

For diffracted light whose angle of emergence is approximately equal toan angle of regular reflection of incident light, if thecenter-to-center distance of the reflection surfaces 22 (in this case,the grating constant of the diffraction grating) is large, differencesbetween the angles of emergence in accordance with the diffraction orderare small. In this case, differences between the angles of emergence inaccordance with the wavelength are also small. If, for example, thereflection surfaces 22 have the length and width in the range of 2 to 50μm and are arranged at intervals in the range of 2 to 50 μm, the reliefstructure RS1 emits diffracted light in the range of angle of about ±19°with respect to the traveling direction of regular reflection light.When the reflection surfaces 22 have the length and width in the rangeof 5 to 50 μm and are arrayed at intervals in the range of 5 to 50 μm,the relief structure RS1 emits diffracted light in the range of angle ofabout ±8° with respect to the traveling direction of regular reflectionlight. Normally, a general light source such as the sun and a room lampis not an ideal point light source. In addition, illumination lightincident on a display include light reflected or scattered by particlesin the air, the ground, floors, and walls. Thus, if the display isobserved in very close range from a direction in which regularreflection light can be observed, diffracted lights of various ordersand wavelengths are incident on eyes of the observer at the same time.

Therefore, the observer perceives a mixed color. If, for example, redlight of the wavelength 630 nm and green light of the wavelength 540 nmare incident on eyes of the observer, the observer perceives yellow.When green light of the wavelength 540 nm and blue light of thewavelength 460 nm are incident on eyes of the observer, the observerperceives cyan, that is, light blue. More concrete examples will bedescribed below.

In a first example, it is assumed for the relief structure RS1 describedwith reference FIG. 5 that the diameter of the reflection surface 22 isabout 10 μm, the ratios S1/S and S2/S are about 50% each, the height ofthe reflection surface 22 relative to the reflection surface 21 is 0.2μm. When the relief structure RS1 is observed from a directionperpendicular to a broken line A or B, the relief structure RS1 can beconsidered as a diffraction grating of the grating constant of about 14μm.

In this case, when the relief structure RS1 is illuminated with whitelight from a direction perpendicular to the reflection surface 21, therelief structure RS1 emits, for example, light of the wavelength of 630nm at an angle of emergence of about 2.58°, light of the wavelength of540 nm at an angle of emergence of about 2.21°, and light of thewavelength of 460 nm at an angle of emergence of about 1.88° in adirection perpendicular to the broken line A or B as +1st-orderdiffracted light. Then, in this case, the relief structure RS1 emitslight of the wavelength of 630 nm at an angle of emergence of about5.16°, light of the wavelength of 540 nm at an angle of emergence ofabout 4.42°, and light of the wavelength of 460 nm at an angle ofemergence of about 3.77° in a direction perpendicular to the broken lineA or B as +2nd-order diffracted light. That is, the relief structure RS1emits diffracted lights of different wavelengths and diffraction ordersin a very small range of angle.

When the relief structure RS1 is observed from a direction perpendicularto, for example, a broken line C, the relief structure RS1 can beconsidered as a diffraction grating of the grating constant a littlesmaller than 14 μm. Thus, if the relief structure RS1 is illuminatedwith white light from a direction perpendicular to the reflectionsurface 21, the relief structure RS1 emits +1st-order diffracted lightand +2nd-order diffracted light at small angels of emergence in adirection perpendicular to the broken line C. Therefore, also in thiscase, the relief structure RS1 emits diffracted lights of differentwavelengths and diffraction orders in a very small range of angle.

In a second example, it is assumed for the relief structure RS1described with reference FIG. 5 that the diameter of the reflectionsurface 22 is about 1 μm and the ratios S1/S and S2/S are about 50%each. When the relief structure RS1 is observed from a directionperpendicular to the broken line A or B, the relief structure RS1 can beconsidered as a diffraction grating of the grating constant of about 1.4μm.

In this case, when the relief structure RS1 is illuminated with whitelight from a direction perpendicular to the reflection surface 21, therelief structure RS1 emits, for example, light of the wavelength of 630nm at an angle of emergence of about 26.7°, light of the wavelength of540 nm at an angle of emergence of about 22.7°, and light of thewavelength of 460 nm at an angle of emergence of about 19.2° in adirection perpendicular to the broken line A or B as +1st-orderdiffracted light. Under normal illumination conditions, as describedabove, a light source is not an ideal point light source. Thus, if therelief structure RS1 is illuminated with white light from a directionperpendicular to the reflection surface 21, the white light is incidenton the relief structure RS1 not only from a normal direction, but alsofrom an oblique direction. When white light is incident on the reliefstructure at an angle of incidence of 1.0° from a directionperpendicular to the broken line C, the relief structure RS1 emits, forexample, light of the wavelength of 630 nm at an angle of emergence ofabout 25.7°, light of the wavelength of 540 nm at an angle of emergenceof about 21.6°, and light of the wavelength of 460 nm at an angle ofemergence of about 18.2° in a direction perpendicular to the broken lineC as +1st-order diffracted light. That is, the relief structure RS1emits diffracted lights of different wavelengths in a very small rangeof angle.

As described above, the relief structure RS1 emits diffracted lights ofdifferent wavelengths in a very small range of angle. Therefore, theobserver perceives a mixed color.

The mixed color perceived by the observer depends further on the heightof the reflection surface 22 relative to the reflection surface 21. Thiswill be described below.

In a diffraction grating, the groove width L and the grating constant dare constant. Therefore, as is evident from the equation (2), thediffraction efficiency η of the diffraction grating can be said to be afunction of the groove depth r (or the protrusion height) and thewavelength λ of illumination light. Based on the above, when consideringthe case of observing the diffraction grating while illuminating thediffraction grating with white light, the fact can be understood thatthe diffraction efficiency of some wavelength band is lower than that ofother wavelength bands and these wavelength bands depend on the groovedepth r. Thus, the color perceived by an observer when a diffractiongrating is illuminated with white light is affected not only by theangle of incidence θ and the grating constant d of illumination lightand the observation direction, but also by the groove depth r.Therefore, the color perceived by the observer when the relief structureRS1 is illuminated with white light is affected by the height of thereflection surface 22 relative to the reflection surface 21.

Different from a general diffraction grating, the relief structure RS1changes its display color not so much when the observation direction ischanged slightly. This will be described below.

As has been described with reference to FIG. 13, when the observerperceives a mixed color, diffracted lights having the same wavelengthand different diffraction orders are incident on eyes of the observer atthe same time. In addition, when the observer perceives a mixed color,diffracted lights having the same wavelength and derived from lightshaving different angles of incidence on the relief structure RS1 areincident on eyes of the observer at the same time. When the observationdirection is changed only slightly, some diffracted light is no longerincident on eyes of the observer, but other diffracted lights having thesame wavelength are incident on eyes of the observer. Therefore,different from a general diffraction grating, the relief structure RS1changes its display color not so much when the observation direction ischanged slightly. Note that when the ratio of the length to the width ofthe reflection surface 22 is brought closer to 1, the change in color inaccordance with the observation angle decreases.

As described above, the relief structure RS1 displays a mixed color as astructural color. When the observation direction is changed slightlyfrom the normal direction, the color displayed by the relief structureRS1 hardly changes. When the observation direction is changedconsiderably from the normal direction, the relief structure RS1 nolonger emits diffracted light. Such a visual effect cannot be achievedby general printed matter, nor can be achieved by a diffraction gratingor hologram, nor can be achieved by a combination of a light-scatteringstructure and a pigmented layer. That is, the relief structure RS1offers an extremely special visual effect.

In each of the relief structures RS1 described with reference to FIGS. 5to 10, the reflection surface 22 has the same shape. Such a reliefstructure is easy to produce.

That is, a master used for the formation of the relief structure RS1 isproduced by a method including a step of writing on a resin layer usinga charged particle beam and a step of subjecting the resin layer todevelopment. According to the method, the depth of recesses or theheight of protrusions is controlled by adjusting the intensity of thecharged particle beam or the irradiation time. When the reflectionsurfaces 22 have different shapes, it is difficult to obtain a reliefstructure in which the depth of recesses or the height of protrusions isuniform even if the intensity of the charged particle beam or theirradiation time is adjusted. In the case where the reflection surfaces22 have the same shape, as compared with the case where the reflectionsurfaces 22 have different shapes, it is easy to obtain a reliefstructure in which the depth of recesses or the height of protrusions isuniform.

When the reflection surfaces 22 have the same shape, it is easy todesign the relief structure RS1. That is, the accurate optical designand optical simulations can be done so that a high-quality master can beproduced with high reproducibility. Therefore, a difference in opticalperformance between the design and a real thing thereof can be minimizedso that stray light can be minimized.

The reflection surfaces 22 may be different in at least one of theshape, dimensions, and center-to-center distance.

FIG. 14 is a plan view schematically showing still another example ofthe first relief structure that can be adopted for the display shown inFIG. 1.

The relief structure RS1 shown in FIG. 14 includes the reflectionsurface 22 having a circular shape, the reflection surface 22 having asmaller circular shape, the reflection surface 22 having an octagonalshape, the reflection surface 22 having a star shape, and the reflectionsurface 22 having a cross shape. These reflection surfaces 22 arearranged irregularly.

Such a relief structure RS1 can be considered to be formed by arrangingmany tiny diffraction gratings having different grating constants.Therefore, the relief structure RS1 emits diffracted lights of variouswavelengths in the same direction. Therefore, the relief structure RS1provides a visual effect almost the same as that described withreference to FIG. 13. The reason why the relief structure RS1 in whichthe reflection surfaces 22 are arranged irregularly provides the abovevisual effect will be described in more detail later.

Moreover, such a structure has the following advantages.

When the reflection surfaces 22 are different in shape, dimension, orcenter-to-center distance, a true-false judgment using the arrangementof the reflection surfaces 22 can be made. When, for example, thereflection surfaces 22 having different shapes are arranged alternately,if such a structure is verified by an observation through an opticalmicroscope for some display, the display can be judged to be anauthentic article. Thus, a person who attempts to produce a forgeryneeds not only to realize a visual effect similar to that of anauthentic article when observed with the naked eye, but also to producethe reflection surfaces 22 in the same shape as that of an authenticarticle. Therefore, such a structure is effective in curbing theproduction of forgeries. Moreover, it is relatively difficult to producesuch a structure and consequently, it is difficult to forge the display1 including such a structure. Therefore, if the above configuration isadopted, the effect of preventing forgeries of the display 1 isincreased.

When the reflection surfaces 22 are arranged regularly, the length andwidth of the reflection surface 22 or the center-to-center distance ofthe reflection surfaces 22 is preferably in the range of 5 to 10 μm. Inthis way, the relief structure RS1 can be caused to emit diffractedlights of various wavelengths in a narrow angular range. Therefore, thedisplay color of the relief structure RS1 can be prevented fromappearing iridescently.

On the other hand, if the reflection surfaces 22 are arrangedirregularly, the length and width of the reflection surface 22 or thecenter-to-center distance of the reflection surfaces 22 is preferably inthe range of 0.3 to 5 μm. As described above, the relief structure RS1in which the reflection surfaces 22 are arranged irregularly can beconsidered to be formed by arranging many tiny diffraction gratingshaving different grating constants. Therefore, the display color of therelief structure RS1 can be prevented from appearing iridescently evenif the length and width of the reflection surface 22 or thecenter-to-center distance of the reflection surfaces 22 is made shorteras compared with the case where the reflection surfaces 22 are arrangedregularly.

When the relief structure RS1 is provided in each of a plurality ofregions, the height of the reflection surface 22 relative to thereflection surface 21 may be made different in some region and otherregions. For example, the height of the reflection surface 22 relativeto the reflection surface 21 may be made different between region of the“O” letter type and the region of the “O” letter type of the region 13shown in FIG. 1. In this manner, the letters “T”, “O”, and “P” can bedisplayed in different colors.

The height of the reflection surface 22 relative to the reflectionsurface 21 may be made different within one region. In this case, amixed color that is difficult to realize when the height of thereflection surface 22 relative to the reflection surface 21 is madeequal within one region and that is difficult to reproduce by forgerycan be displayed.

The reflection surface 22 preferably has a circular shape or polygonalshape with five vertices or more, particularly a regular polygonalshape. An optical effect exhibited by the relief structure RS1 adoptingsuch a configuration is less dependent on an azimuth angle of theobservation direction. The “azimuth angle” is used herein assuming polarcoordinates in which the polar axis is perpendicular to the reflectionsurface 21. Therefore, when the illumination direction or observationdirection changes, the display color hardly changes.

The reason why the relief structure RS1 in which the reflection surfaces22 are arranged irregularly provides the above visual effect will bedescribed with reference to FIGS. 15 and 16.

FIG. 15 is a diagram schematically showing the situation in which thefirst relief structure having the second reflection surfaces irregularlyarranged displays a mixed color as a structural color. FIG. 16 is adiagram schematically showing the situation in which lights reflected bythe first and second reflection surfaces interfere with each other.

As described above, the relief structure RS1 in which the reflectionsurfaces 22 are arranged irregularly can be considered to be formed byarranging many tiny diffraction gratings having different gratingconstants. Thus, as shown in FIG. 15, if the display 1 is illuminatedwith the illumination light IL, the relief structure RS1 reflects theregular reflection light RL and also emits the diffracted light DLhaving the same wavelength in various directions.

When the illumination light IL is incident on the relief structure RS1at an angle θ, as shown in FIG. 16, the optical path difference betweenlight RL2 reflected by the reflection surface 22 and light RL1 reflectedby the reflection surface 21 is twice the product of the height r of thereflection surface 22 relative to the reflection surface 21 and the cosθ. Therefore, if the refractive index of the light-transmitting layer 11is n, the phase difference of these lights is the product of 2π/λ and 2rcos θ.

When the phase difference is an integral multiple of 2π, the light RL1and the light RL2 cause constructive interference. In this case,therefore, the relief structure RS1 emits the regular reflection lightRL at high intensity and the diffracted light DL at low intensity.

On the other hand, when the phase difference is equal to the sum of avalue obtained by multiplying 2π by an integer and n, the light RL1 andthe light RL2 cause destructive interference. In this case, therefore,the relief structure RS1 emits the regular reflection light RL at lowintensity and the diffracted light DL at high intensity.

Incidentally, a general relief structure that displays a structuralcolor, for example, a diffraction grating or a light-scatteringstructure has the depth of a recess or the height of a protrusion set toabout 0.1 μm. When the visible region is 380 to 780 nm, such a recess orprotrusion generates an optical path difference about half thewavelength by reflecting visible light. That is, the phase differencecaused by such a recess or protrusion is not such that diffractionefficiency in a partial wavelength band in the wavelength range of thevisible region is significantly decreased as compared with thediffraction efficiency in other wavelength bands.

However, if the depth of the recess or the height of the protrusionreaches a certain level of magnitude, lights of certain wavelengths inthe visible region cause constructive interfere and lights of otherwavelengths cause destructive interfere. As a result, diffractionefficiency in a partial wavelength band in the wavelength range of thevisible region becomes significantly smaller than the diffractionefficiency in other wavelength bands.

As has been described with reference to FIG. 15, the relief structureRS1 in which the reflection surfaces 22 are arranged irregularly can beconsidered to be formed by arranging many tiny diffraction gratingshaving different grating constants. Thus, the relief structure in whichrecesses or protrusions are arranged irregularly emits diffracted lightshaving different wavelengths in the same direction.

Therefore, the relief structure RS displays a mixed color as astructural color. The mixed color displayed by the relief structure RShardly changes when the observation direction is slightly changed.

This effect is affected by the degree of order of the arrangement of thereflection surfaces 22. Though the complete disorder is ideal, such astructure is difficult to design and produce. Therefore, as will beillustrated below, it is desirable to determine the arrangement of thereflection surfaces 22 by considering the usage form of the display 1.

When an image displayed by the display 1 is observed in a situation inwhich the light source has a dimension of about 5 cm like a bulb and thedistance from the light source to the display 1 is about 2 m, the angleof incidence of illumination light varies in the angular range of about1.5°. Under such conditions, a diffraction grating whose gratingconstant is 20 μm or more can emit diffracted light in the samedirection for all wavelengths in the visible region. Therefore, if thereflection surfaces 22 are arranged irregularly in all regions of thediameter of 20 μm or more, such a relief structure RS1 does not displaya chromatic color originating from a periodic structure.

It is desirable to observe a mixed color originating from theconstructive interference and the destructive interference under theconditions under which regular reflection light is not incident on eyesof the observer. Therefore, a larger angle of divergence of diffractedlight is desirable.

The intensity distribution of diffracted light can be represented by thefollowing equation (3).

I _(N)=sin²[π/λ×(sin Φ)×a]  (3)

In the equation, I_(N) denotes the normalized intensity of diffractedlight, a denotes the average dimension of the reflection surface 21 or22, and ϕ denotes the angle of emergence of diffracted light. The angleof divergence is the minimum angle of emergence ϕ when the intensityI_(N) represented by the equation (3) becomes zero. That is, the angleof divergence is the angle of emergence ϕ satisfying sin ϕ=λ/a.

Under normal observation conditions, if the angle of divergence is about20° or more, the display of the mixed color is not hindered by regularreflection light. The visible region is centered around about 500 nm andthus, 500 nm is used here as the wavelength λ. In this case, if thedimension a is 1.5 μm or less, the angle of divergence is about 20° ormore can be realized.

Next, the depth or height of the reflection surface 22 relative to thereflection surface 21 will be described.

The intensity of light at which light reflected by the reflectionsurface 21 and light reflected by the reflection surface 22 do notinterfere is approximately proportional to a value calculated from thefollowing equation (4).

$\begin{matrix}{\sin^{2}\frac{2\; \pi \times n \times r \times \cos \; \theta}{\lambda}} & (4)\end{matrix}$

Therefore, the color of diffracted light can approximately be calculatedby using color matching functions x(λ), y(λ), and z(λ) and calculatingthree stimulus values X, Y, and Z according to the following equations(5) to (7).

$\begin{matrix}{X = {\int\lbrack {{x(\lambda)} \times ( {\sin^{2}\frac{2\; \pi \times n \times r \times \cos \; \theta}{\lambda}} ) \times r \times \lambda} \rbrack}} & (5) \\{Y = {\int\lbrack {{y(\lambda)} \times ( {\sin^{2}\frac{2\; \pi \times n \times r \times \cos \; \theta}{\lambda}} ) \times r \times \lambda} \rbrack}} & (6)\end{matrix}$

For the height or depth r ranging from 0.10 to 0.30 μm, the color ofdiffracted light is calculated by assuming that the angle of incidence θand the refractive index n are 30° and 1.5, respectively. The result ofcalculation is shown in FIG. 17.

FIG. 17 is a u′v′ chromaticity diagram showing an example of colorchanges caused when the difference between the heights of the reflectionsurfaces 21 and 22 is changed in the range of 0.10 to 0.30 μm. In FIG.17, a white circle indicates the display color when the differencebetween the heights of the reflection surfaces 21 and 22 is zero, thatis, white.

As shown in FIG. 17, when the difference between the heights of thereflection surfaces 21 and 22 is about 0.10 μm, white is displayed. Whenthe difference between the heights is about 0.15 μm, yellow isdisplayed. When the difference between the heights is further increased,chromaticity coordinates rotate around the white chromaticitycoordinate. Therefore, it is desirable to set the difference between theheights of the reflection surfaces 21 and 22 to about 0.15 μm or morefor the display of chromatic colors.

When the difference between the heights is continuously changed from0.15 to 0.30 μm, chromaticity coordinates make an approximate round ofthe white chromaticity coordinate. That is, by setting the differencebetween the heights to the range of 0.15 to 0.30 μm, all colors can berepresented. However, the intensity of green is relatively low.

Next, color changes caused when the difference between the heights ofthe reflection surfaces 21 and 22 is changed in other ranges under thesame conditions as the above conditions. The result thereof is shown inFIGS. 18 and 19.

FIG. 18 is a u′v′ chromaticity diagram showing an example of colorchanges caused when the difference between the heights of the reflectionsurfaces 21 and 22 is changed in the range of 0.30 to 0.50 μm. FIG. 19is a u′v′ chromaticity diagram showing an example of color changescaused when the difference between the heights of the reflectionsurfaces 21 and 22 is changed in the range of 0.50 to 0.70 μm.

As shown in FIG. 18, when the difference between the heights of thereflection surfaces 21 and 22 is continuously changed in the range of0.30 to 0.50 μm, chromaticity coordinates make an approximate round ofthe white chromaticity coordinate. That is, by setting the differencebetween the heights to the range of 0.30 to 0.50 μm, all colors can berepresented. Moreover, in this case, green can be displayed atrelatively high intensity.

As shown in FIG. 19, when the difference between the heights of thereflection surfaces 21 and 22 is set within the range of 0.50 to 0.70μm, the green and purple colors can be displayed at relatively highintensity. In this case, however, other colors cannot be displayed athigh intensity.

It is difficult to form the relief structure RS1 in which the differencebetween the heights of the reflection surfaces 21 and 22 is large.Therefore, in consideration of points described with reference to FIGS.17 to 19 and ease of production, the difference between the heights ofthe reflection surfaces 21 and 22 is preferably set to the range of 0.15to 0.50 μm, and more preferably set to the range of 0.15 to 0.50 μm.

It becomes more difficult to form the relief structure RS1 with anincreasing ratio of the difference between the heights of the reflectionsurfaces 21 and 22 to the dimension of the reflection surfaces 22. Inaddition, it becomes more difficult to form the relief structure RS1with an increasing ratio of the difference between the heights of thereflection surfaces 21 and 22 to the distance between the reflectionsurfaces 22. The ratio is preferably 1 or less. The difference betweenthe heights of the reflection surfaces 21 and 22 is preferably 0.50 μmor less and thus, the dimension of the reflection surface 22 ispreferably 0.50 μm or more and the distance between the reflectionsurfaces 22 is preferably 0.50 μm or more. Therefore, thecenter-to-center distance of the reflection surfaces 22 is preferably1.0 μm or more.

Next, calculation results carried out regarding the angle of incidenceof illumination light and the display color will be described.

As described above, the optical path difference between light reflectedby the reflection surface 22 and light reflected by the reflectionsurface 21 is expressed as 2nr cos θ. As is evident from the formula,the display color can be affected not only by the difference between theheights of the reflection surfaces 21 and 22, but also by the angle ofincidence θ at which illumination light propagating through thelight-transmitting layer 11 is incident on the relief structure RS1.

The angle of incidence θ can be determined from an angle of incidence θ₀at which illumination light propagating through the air is incident onthe resin layer 11 by using the Snell's law. By using the angle ofincidence θ obtained in this manner, color changes caused when the angleof incidence θ₀ is continuously changed from 0° to 90° are investigatedby the same method as described above. In this case, the refractiveindex n of the resin layer 11 and the difference r between the heightsof the reflection surfaces 21 and 22 are assumed to be 1.5 and 0.30 μm,respectively. The result thereof is shown in FIGS. 20 and 21.

FIG. 20 is a u′v′ chromaticity diagram showing an example of colorchanges caused when the angle of incidence θ₀ of illumination light iscontinuously changed in the range of 0° to 90°. FIG. 21 is a u′v′chromaticity diagram showing an example of color changes caused when theangle of incidence θ₀ of illumination light is continuously changed inthe range of 20° to 40°.

As shown in FIG. 20, when the angle of incidence θ₀ is changed from 0°to 90°, the display color changes from orange to cyan. That is, if theangle of incidence θ₀ is significantly changed, the change of thedisplay color can be perceived.

As shown in FIG. 21, when the angle of incidence θ₀ is changed from 20°to 40°, the change of the display color in accordance with the angle ofincidence θ₀ is small. In this range, the display color is yellowregardless of the angle of incidence θ₀. That is, when the angle ofincidence θ₀ changes slightly under normal observation conditions, thedisplay color of the relief structure RS1 does not change. Therefore,under normal observation conditions, the display color of the reliefstructure RS1 does not change when the observation direction changesslightly.

A diffraction grating or a light-scattering structure similar to therelief structure RS1 has been known, but such a diffraction grating orlight-scattering structure does not shows the above coloring effect.This will be described below.

FIG. 22 is a sectional view schematically showing an example of thediffraction grating. FIG. 23 is a sectional view schematically showinganother example of the diffraction grating.

The diffraction gratings RS shown in FIGS. 22 and 23 are reliefstructures. These diffraction gratings RS have a structure in which aplurality of grooves GR are arranged in the width direction. In each ofthe diffraction gratings RS, the width of the groove GR and the distancebetween center lines are constant.

The diffraction grating RS shown in FIG. 22 has a section perpendicularto the length direction of the groove GR in a sinusoidal shape. On theother hand, the diffraction grating RS shown in FIG. 23 has a sectionperpendicular to the length direction of the groove GR in a rectangularwave shape.

The diffraction grating RS shown in FIG. 22 does not contain any planecorresponding to the reflection surfaces 21 and 22. Thus, thelight-scattering structure RS does not show the coloring effectdescribed by using the above formula.

The diffraction grating RS shown in FIG. 23 contains reflection surfaces21′ and 22′ corresponding to the reflection surfaces 21 and 22, but isnot formed with precision in shape sufficient to show the coloringeffect described by using the above formula. More specifically, thereflection surfaces 21′ and 22′ have fine relief or the height of thereflection surface 22′ relative to the reflection surface 21′ isnon-uniform. This results from the facts that it is difficult to form adiffraction grating or light-scattering structure with precision inshape sufficient to show the coloring effect described by using theabove formula by a normal production process and high precision in shapeis not required particularly for the light-scattering structure andrather, an irregular shape is advantageous in terms of light-scatteringpower.

The diffraction grating is generally used for spectral purposes. Thediffraction grating used for such spectral purposes does not normallyadopt a configuration in which diffracted lights having differentwavelengths are emitted in a narrow angular range.

In a general relief-type light-scattering structure, the depth of therecess or the height of the protrusion is 0.1 μm or less. In such acase, the coloring effect described by using the above formula cannot beobtained. That is, in such a case, an effect of making the diffractionefficiency in a partial wavelength band in the wavelength range of thevisible region, for example, about 380 nm to about 700 nm or about 380nm to about 780 nm sufficiently smaller than the diffraction efficiencyin other wavelength bands is not obtained.

(Second Relief Structure)

As shown in FIG. 2, the second relief structure RS2 is provided on thesurface of the relief structure formation layer 112. The second reliefstructure RS2 displays a structural color. The second relief structureRS2 shows an optical effect different from that of the first reliefstructure RS1. Incidentally, the second relief structure RS2 may beomitted.

The second relief structure RS2 is, for example, a diffraction gratingor a hologram. Alternatively, the second relief structure RS2 is alight-scattering structure that displays an achromatic color regardlessof the observation direction. Alternatively, the second relief structureRS2 is a light-absorbing structure. Alternatively, the second reliefstructure RS2 is a combination of at least two of the above. Thelight-scattering structure and the light-absorbing structure will bedescribed later with reference to drawings.

As described above, the second relief structure RS2 shows an opticaleffect that is different from the optical effect of the first reliefstructure RS1. Thus, in the case where the second relief structure RS2is provided, compared with a case where the second relief structure RS2is omitted, characteristic optical effects shown by the first reliefstructure RS1 are conspicuous. Moreover, if the second relief structureRS2 is provided, a more complex visual effect can be achieved, making aforgery of the display 1 more difficult.

More specifically, if the display 1 contains a diffraction structuresuch as a diffraction grating and hologram as the second reliefstructure RS2, the display 1 can be caused to display iridescentspectral colors. Also in this case, image switching as described abovecan be realized and the second relief structure RS2 can be caused todisplay a stereoscopic image by using changes in wavelength andintensity of diffracted light in accordance with the illuminationdirection and the observation direction.

The grating constant of the diffraction grating is, for example, in therange of 0.3 to 3 μm. The depth of groove of the diffraction grating is,for example, 0.1 μm or less.

When a light-absorbing structure or a light-scattering structure thatdisplays an achromatic color regardless of the observation direction isadopted to the second relief structure RS2, the following visual effectis obtained.

FIG. 24 is a perspective view schematically showing an example of thestructure that can be adopted for the second relief structure. FIG. 25is a perspective view schematically showing another example of thestructure that can be adopted for the second relief structure.

The second relief structure RS2 shown in FIG. 24 is a light-absorbingstructure. The second relief structure RS2 contains a plurality ofprotrusions or recesses 23 each having a tapered shape. In FIG. 24, asan example, protrusions in a substantially conical shape are depicted asthe protrusions or recesses 23. The shape of the protrusions or recesses23 may be pyramidal.

The protrusions or recesses 23 are arranged two-dimensionally with acenter-to-center distance shorter than the shortest wavelength of thevisible region or with a center-to-center distance of 400 nm or less. Itis assumed here, as an example, that the protrusions or recesses 23 arearranged regularly in the X and Y directions.

The height or depth of the protrusions or recesses 23 is, for example,300 μm and typically in the range of 300 μm and 450 μm. When thecenter-to-center distance is sufficiently short, an antireflectioneffect increases with an increasing height or depth. However, it isdifficult to form the protrusions or recesses 23 that are too high ordeep with high precision.

The protrusions or recesses 23 are arranged regularly. In this case,when the relief structure RS2 is illuminated with white light from anoblique direction, the relief structure RS2 does not emit diffractedlight in the angular range in which regular reflection light isobservable and instead, emits diffracted light in the angular range inwhich regular reflection light is not observable. That is, if the angleof normal of the display surface is 0° and the angular range includingthe illumination direction is defined as the positive angular range, therelief structure RS2 does not emit diffracted light in the negativeangular range and instead, emits diffracted light in the positiveangular range. That is, the relief structure RS2 in which theprotrusions or recesses 23 are arranged regularly displays an achromaticcolor, for example, a dark gray or black under normal observationconditions and displays spectral colors under special observationconditions.

The arrangement of the protrusions or recesses 23 may be irregular. Insuch a case, the relief structure RS2 displays, for example, a dark grayor black regardless of observation conditions.

The relief structure RS2 shown in FIG. 25 is a light-scatteringstructure. The relief structure RS2 contains a plurality of protrusionsor recesses 24. In FIG. 25, as an example, protrusions in a taperedshape are depicted as the protrusions or recesses 24. The protrusions orrecesses 24 have various dimensions and shapes and are arrangedirregularly. Many of the protrusions or recesses 24 have the maximumdimension perpendicular to the Z axis of, for example, 3 μm or more andthe dimension in the Z direction of, for example, 1 μm or more. When therelief structure RS2 is illuminated with white light, the reliefstructure RS2 displays an achromatic color, for example, whiteregardless of the illumination direction and the observation direction.

When the protrusions or recesses 24 are arranged irregularly, at leastone of the dimension and shape may be equal. The protrusions or recesses24 may have a shape extending in one direction perpendicular to the Zdirection. In this manner, a light-scattering anisotropy can be providedto the relief structure RS2. That is, in this case, light-scatteringpower of the relief structure RS2 is changed when the display 1 isrotated around an axis parallel to the Z axis while illuminating thedisplay 1 from an oblique direction.

The above display 1 is produced by, for example, the following method.

First, formed is the relief structure formation layer 112 having therelief structure RS1 and the relief structure RS2 provided on thesurface of the substrate 111.

To obtain the above effect regarding the relief structure RS1, it isnecessary to form the relief structure RS1 with extremely highprecision. The relief structure RS1 superior in shape precision anddimension precision can be formed by one of the first to third methodsdescribed below.

According to the first method, first, a resin layer having a uniformthickness is formed on a smooth surface. As the material of the resinlayer, for example, a material insolubilized or solubilized for adeveloper by irradiation with a charged particle beam such as anelectron beam. Next, a predetermined pattern is formed on the resinlayer by a charged particle beam such as an electron beam. Then, theresin layer is subjected to development to obtain a patterncorresponding to the reflection surface 21 or 22.

The top surface of the pattern obtained in this manner has a reliefwhose depth or height is, for example, 10 nm. Then, the pattern isheated to smooth the top surface. To cause a thermal flow only on thetop surface, a hot air of 100° C. to 150° C. is blown on the top surfaceof the pattern. The heating is complete in a short time such as 1 to 5seconds so that the shape of the side surface of the pattern should notchange considerably. The heating is carried out by, for example, coolingthe pattern from the undersurface side.

The second method is the same as the first method except that smoothingis done by the following method. That is, according to the secondmethod, a pattern having a relief on the upper side thereof is subjectedto ashing using, for example, oxygen plasma. This removes a portion ofthe top surface of the pattern to smooth the top surface.

The first and second methods are simple, but optimization of conditionsand the like is not easy. According to the third method described below,though the production process becomes more complex, high shape precisionand dimension precision can be realized more easily.

The third method is the same as the first method except that smoothingis done by the following method. That is, according to the third method,after forming a pattern having an opening and a top surface with surfaceasperities, a second material having a higher softening point than afirst material constituting the pattern is applied to the entiresurface. Accordingly, the opening of the pattern is filled with thesecond material. Next, the surface of the film of the second material ispolished until the top surface of the pattern made of the first materialis exposed. Then, a flat plate having a smooth surface is heated to atemperature equal to or higher than the softening point of the firstmaterial and lower than the softening point of the second material whilepressing the flat plate against the pattern made of the first materialand the film made of the second material. Accordingly, a thermal flow ofthe first material on the top surface of the pattern is caused. Next,the first material is sufficiently cooled while the flat plate beingpressed. After the first material is completely set, the flat plate isremoved and further, the film made of the second material is removed. Inthis manner, a pattern having a smooth top surface is obtained.

A pattern obtained according to one of the above methods can be useditself as at least a portion of the relief structure formation layer112. Alternatively, it is possible to produce a metallic stamper fromthe master by electroforming or the like using a structure obtainedaccording to one of the above methods as a master and form the reliefstructure formation layer 112 using the stamper. The electroforming is akind of surface treatment technique that forms a metal film on an objectby reducing metallic ions on the surface of the object immersed in apredetermined aqueous solution. By using the above methods, a finerelief structure provided on the surface of a master can be duplicatedwith precision. Incidentally, the surface of an object on whichelectroforming is performed needs to be electrically conducting.Generally, a photosensitive resist does not conduct electricity andthus, a thin metal film is provided on the surface of the object byvapor phase deposition such as sputtering and vacuum evaporation beforeelectroforming.

Next, the stamper is used to duplicate the relief structures RS1 andRS2. That is, first, a thermoplastic resin or a photo-curable resin isapplied onto the substrate 111 made of, for example, polycarbonate orpolyester. Next, the metallic stamper is brought into close contact withthe applied film and in this state, the resin layer is heated orirradiated with light. After the resin being set, the metallic stamperis removed from the set resin. Accordingly, the relief structureformation layer 112 provided with the relief structures RS1 and RS2 isobtained.

Next, a single layer or a plurality of layers of a metal such asaluminum or a dielectric is deposited on the relief structure formationlayer 112 by, for example, evaporation method. Accordingly, thereflection layer 12 is obtained. In this way, the display 1 iscompleted.

Second Embodiment

Next, the second embodiment of the present invention will be described.

A display according to the second embodiment is the same as the display1 according to the first embodiment except that a structure describedbelow is adopted for a region 13.

FIG. 26 is a plan view schematically showing an example of the structurethat can be adopted for a display according to the second embodiment ofthe present invention. FIG. 27 is an enlarged plan view showing aportion of the structure shown in FIG. 26. FIG. 28 is a sectional viewtaken along an XXI-XXI line of the structure shown in FIG. 26.

FIG. 26 depicts pixels PX arranged regularly in the X and Y directions.Each pixel PX has a right-angle quadrangular shape, for example, asquare shape. As will be described later, some pixels PX include arelief structure RS1 and other pixels PX include a relief structure RS2.

The pixel PX is designed so that the longest side thereof has adimension in the range of 3 μm to 300 μm. When the dimension of thepixel PX is large, an image cannot be displayed in high resolution. Whenthe dimension of the pixel PX is small, it becomes difficult to form asufficient number of protrusions or recesses with precision in the pixelPX.

The pixels PX arranged in the region 13 include the relief structureRS1. The relief structure RS1 is the same as the relief structure RS1described with reference to FIGS. 5 and 6.

On the other hand, the pixels PX arranged in a region 17 include therelief structure RS2. The relief structure RS2 here is a diffractiongrating in which the length direction of groove is inclined to the Xdirection.

In the region 13, a ratio S/S0 of an area S of the relief structure RS1to an area S0 of the pixel PX is different from place to place. FIG. 26depicts three pixels PX having different ratios S/S0.

The contour of the pixel PX is determined based on the arrangementdirection and period of the relief structure RS1 and an arrangementpattern of a reflection surface 22. In this case, the arrangementdirection, period, and shape of the relief structure RS2 may beconsidered if necessary. The contour of the relief structure RS1 isassumed, as shown in FIG. 27, to be a polygon of a minimum area ofpolygons enclosing all the reflection surfaces 22 contained in therelief structure RS1 and whose interior angles are all less than 180°.

The relief structure RS1 is positioned in the center of the pixel PX.The relief structure RS1 may not be positioned in the center of thepixel PX. The position of the relief structure RS1 relative to thecenter of the pixel PX may be equal or different among the pixels PX.

Two or more of the pixels PX having the equal ratio S/S0 have the equalheight or depth of the reflection surface 22 relative to a reflectionsurface 21. Then, two or more of the pixels PX having different ratiosS/S0 have, as shown in FIG. 28, mutually different heights or depths ofthe reflection surface 22 relative to the reflection surface 21.

The radio S/S0 affects the saturation of color displayed by the pixelPX. The height or depth of the reflection surface 22 relative to thereflection surface 21 affects the hue of color displayed by the pixelPX. Therefore, if the above configuration is adopted, a more complexdisplay can be made.

The pixels PX can be arranged in various ways.

FIG. 29 is a plan view schematically showing an example of thearrangement of pixels. FIG. 30 is a plan view schematically showinganother example of the arrangement of pixels.

In FIG. 29, the pixels PX each having a rectangular shape are arrangedin a direction inclined to the X direction and in the Y direction. InFIG. 30, the pixels PX each having a hexagonal shape are arranged in adirection inclined to the X direction and in the Y direction. When thepixels PX in the same shape are arranged two-dimensionally and regularlyas above, it is easy to design a display 1 and also easy to produce thedisplay 1 on demand. The display 1 may contain a plurality of regionsthat are different in at least one of shape and arrangement of thepixels PX.

The pixel PX may have other shapes. For example, the pixel PX may have aquadrangular shape other than the square and rectangular shapes such asa parallelogram. Alternatively, the pixel PX may have a triangularshape. The pixels PX having these shapes can be arranged without gap.

Two arrangement directions of the pixels PX may be oblique to each otheror perpendicular to each other.

When the structure described with reference to FIGS. 26 to 28 isadopted, gradations in hue and saturation can be realized.

FIG. 31 is a diagram schematically showing examples of images that canbe displayed by the display according to the second embodiment of thepresent invention.

The display 1 shown in FIG. 31 displays images IG1 to IG3. In portionscorresponding to the images IG1 to IG3 of the display 1, the ratio S/S0of the area S of the relief structure RS1 to the area S0 of the pixel PXis different from place to place. The pixels PX having the equal ratioS/S0 have the equal height or depth of the reflection surface 22relative to the reflection surface 21. The pixels PX having the equalratio S/S0 have mutually different heights or depths of the reflectionsurface 22 relative to the reflection surface 21.

More specifically, in the portion corresponding to the image IG1 of thedisplay 1, the ratio S/S0 decreases from left to right. For example,pixels PX each having the same structure as that of the pixel PX shownat the upper left of FIG. 26 are arranged at the left-edge region, pixelPX each having the same structure as that of the pixel PX shown at theupper right of FIG. 26 are arranged at the right-edge region, and thepixels PX each having the same structure as that of the pixel PX shownat the lower left of FIG. 26 are arranged in the intermediate region.The height or depth of the reflection surface 22 relative to thereflection surface 21 decreases from left to right in this portion.Therefore, the saturation decreases from left to right in the image IG1while changing the hue.

In the portion corresponding to the image IG2 of the display 1, theratio S/S0 decreases from the circumference to the center. For example,pixels PX each having the same structure as that of the pixel PX shownat the upper left of FIG. 26 are arranged in the circumferential region,pixels PX each having the same structure as that of the pixel PX shownat the upper right of FIG. 26 are arranged in the center region, andpixels PX each having the same structure as that of the pixel PX shownat the lower left of FIG. 26 are arranged in the intermediate region.The height or depth of the reflection surface 22 relative to thereflection surface 21 decreases from the circumference to the center inthis portion. Therefore, the saturation decreases from the circumferenceto the center in the image IG2 while changing the hue.

In the portion corresponding to the image IG3 of the display 1, theratio S/S0 decreases from left to right. For example, pixels PX eachhaving the same structure as that of the pixel PX shown at the upperleft of FIG. 26 are arranged at the left-edge region, pixels PX eachhaving the same structure as that of the pixel PX shown at the upperright of FIG. 26 are arranged at the right-edge region, and pixels PXeach having the same structure as that of the pixel PX shown at thelower left of FIG. 26 are arranged in the intermediate region. Theheight or depth of the reflection surface 22 relative to the reflectionsurface 21 decreases from left to right in this portion. Therefore, thesaturation decreases from left to right in the image IG3 while changingthe hue.

Thus, if the above configuration is adopted, a more complex display canbe made. It is more difficult to forge the display 1 that displays suchan image.

In the above configuration, as compared with the pixel PX having asmaller ratio S/S0, the pixel PX having a larger ratio S/S0 has agreater height or depth of the reflection surface 22 relative to thereflection surface 21. Conversely, as compared with the pixel PX havinga smaller ratio S/S0, the pixel PX having a larger ratio S/S0 may have asmaller height or depth of the reflection surface 22 relative to thereflection surface 21. However, if the height or depth of the reflectionsurface 22 relative to the reflection surface 21 is made smaller, thediffraction efficiency decreases. Therefore, in order to change thesaturation significantly, the pixel PX having a larger ratio S/S0preferably has a greater height or depth of the reflection surface 22relative to the reflection surface 21 as compared with the pixel PXhaving a smaller ratio S/S0.

Here, as an example, the reflection surfaces 22 each having a circularshape are regularly arranged in each of the relief structures RS1.Similar to the first embodiment, the reflection surface 22 may havedifferent shapes.

Third Embodiment

Next, the third embodiment of the present invention will be described.

A display according to the third embodiment is the same as the display 1according to the first or second embodiment except that a print layer iscontained.

FIG. 32 is a sectional diagram schematically showing an example of thestructure that can be adopted for a display according to the thirdembodiment of the present invention. FIG. 33 is a sectional diagramschematically showing another example of the structure that can beadopted for a display according to the third embodiment of the presentinvention. FIG. 34 is a sectional diagram schematically showing stillanother example of the structure that can be adopted for a displayaccording to the third embodiment of the present invention.

The display 1 shown in FIGS. 32 to 34 has a print layer 14 provided at aposition corresponding to a region 17. As shown in FIG. 32, the printlayer 14 may be provided to face a relief structure formation layer 112with a substrate 111 interposed therebetween. Alternatively, the printlayer 14 may be provided, as shown in FIG. 33, between the reliefstructure formation layer 112 and a reflection layer 12. Alternatively,as shown in FIG. 34, the print layer 14 may be provided to face therelief structure formation layer 112 with the reflection layer 12interposed therebetween.

As shown in FIGS. 32 and 34, the relief structure may be omitted fromthe surface of the relief structure formation layer 112 at the positionof the print layer 14. Alternatively, as shown in FIG. 33, the reliefstructure may be provided on the surface of the relief structureformation layer 112 at least at a portion of the region corresponding tothe print layer 14. As shown in FIG. 34, at least a portion of thereflection layer 12 may be omitted at the position of the print layer14.

When the print layer 14 is provided between the relief structureformation layer 112 and the reflection layer 12 as shown in FIG. 33, therefractive index of the print layer 14 is preferably approximately equalto that of the material constituting the relief structure formationlayer 112. In this case, a portion of the relief structure in contactwith the print layer 14 can be prevented from displaying a structuralcolor.

When the reflection layer 12 and the print layer 14 are formed on therelief structure formation layer 112 in this order as shown in FIG. 34,the reflection layer 12 is formed, for example, such that the reflectionlayer 12 covers only a portion of the surface of the relief structureformation layer 112. In this case, the print layer 14 is formed, forexample, such that the print layer 14 at least partially covers theregion of the surface of the relief structure formation layer 112 wherethe reflection layer 12 is not formed. In this case, even if thereflection layer 12 does not have light-transmitting properties, animage corresponding to a pattern of the print layer 12 can be perceivedby observing the display 1 from the side on the substrate 111.

The print layer 14 displays, for example, images such as letters,patterns, and symbols. The print layer 14 is formed of ink or toner anddisplays chromatic colors or achromatic colors having hue, lightness,and saturation specific to the ink or toner.

As the ink, for example, offset printing ink, letterpress ink, orrotogravure ink is used in accordance with the printing method. The inkused for printing can be classified by composition like resin-type ink,oil-based ink, and water-based ink. Alternatively, the printing ink canbe classified by method of drying like oxidative polymerization ink,penetration-drying ink, evaporation-drying ink, and UV-curing ink. Theprinting ink is selected appropriately in accordance with the type ofsubstrate and the printing method.

As the toner, for example, plastic particles having electrostaticproperties to which color particles such as graphite and pigments areadhere are used. The print layer 14 may be formed by causing such tonerto transfer to a substrate such as a polyethylene terephthalate (PET)film and paper by using static electricity and fusing the toner byheating.

When common printing ink or toner is used, the display color of theprint layer 14 does not change significantly in accordance with theangle of incidence of illumination light or the observation direction.On the other hand, the relief structure RS1 displays the structuralcolor when observed from the normal direction and does not display thestructural color when observed at a small angle with respect to thedisplay surface. Thus, by comparing the display color of the print layer14 with the display color of the relief structure RS1, features thereofare made conspicuous. Therefore, a high level of forgery preventioneffect can be realized by combining the relief structure RS1 and theprint layer 14.

By appropriately combining the type of ink or toner, the concentrationof pigment or dye, and the printing method, the identification of aregion 13 and the region 17 of the display 1 may be made impossible ordifficult when observed, for example, from the normal direction. Thatis, the display 1 may be configured such that the region 13 and theregion 17 display approximately the same color when observed, forexample, from the normal direction. As described above, the region 13does not change the display color when the observation direction ischanged slightly from the normal direction. However, if the angle of theobservation direction formed with the display surface is sufficientlysmall, the region 13 displays a thinner structural color or does notdisplay the structural color. Thus, in this case, the region 13 and theregion 17 can be discriminated from each other.

That is, the print layer 14 and the relief structure RS1 display alatent image when the print layer 14 and the relief structure RS1 areilluminated with white light from, for example, the normal direction andregular reflection light is observed. Then, the print layer 14 and therelief structure RS1 display a visible image when the print layer 14 andthe relief structure RS1 are illuminated with white light from anoblique direction and regular reflection light is observed. Therefore,by adopting the above configuration, a more complex visual effect can beachieved.

An example of such a visual effect will be described with reference toFIGS. 35 and 36.

FIG. 35 is a plan view schematically showing an example of the imagedisplayed by the display according to the third embodiment of thepresent invention when an observer observes it from the normaldirection. FIG. 36 is a perspective view schematically showing anexample of the image displayed by the display shown in FIG. 35 when anobserver observes it from an oblique direction.

The display 1 shown in FIGS. 35 and 36 is the same as the display 1described with reference to FIGS. 1 and 2 except that the followingconfiguration is adopted. That is, the display 1 does not contain aregion 18, and the region 17 is provided with the print layer 14described with reference to FIGS. 32 to 34. The print layer 14 is formedof normal ink or toner and hardly causes the change in color inaccordance with the observation direction. When the display 1 isobserved from the normal direction, as shown in FIG. 35, approximatelythe same color is displayed by the region 13 and the region 17.

When the observation direction of the display 1 is sufficientlyinclined, as shown in FIG. 36, the display color of the region 13changes. That is, a latent image is visualized by inclining theobservation direction sufficiently.

Functional ink whose color changes in accordance with the wavelength ofillumination light or the observation direction may be used as printingink. As the functional ink whose color changes in accordance with thewavelength of illumination light, for example, fluorescent ink orphosphorescent ink can be used. As the functional ink whose colorchanges in accordance with the observation direction, for example,optically variable ink, color shift ink, pearl ink, or retroreflectiveink can be used.

The fluorescent ink is ink including a fluorescent pigment. Thefluorescent ink displays a specific color when irradiated withultraviolet rays. The phosphorescent ink emits light in a dark place fora long time after being stimulated by light.

The optically variable ink and color shift ink make a color change, forexample, from red to green or from blue to purple in accordance with theobservation direction. The pearl ink displays a pale pearl color whenobserved from a specific direction. The retroreflective ink reflectsillumination light in a direction approximately equal to the incidentdirection with a high reflectivity.

For persons who are unfamiliar with an act of making a true-falsejudgment using the color change of the region 13, a true-false judgmentusing the color change of the region 17 is easy. When the true-falsejudgment using the color change of the region 13 and the true-falsejudgment using the color change of the region 17 are combined, a morereliable true-false judgment can be made. Particularly, if the displaycolor of the region 17 changes in accordance with the observationdirection, the observer can be made to perceive color changes of boththe region 13 and the region 17 at the same time by causing theobservation angle at which the display color of the region 13 changesand the angle at which the display color of the region 17 changes toapproximately match. Therefore, a more reliable true-false judgment canbe made.

An example of such a visual effect will be described with reference toFIGS. 37 and 38.

FIG. 37 is a plan view schematically showing another example of theimage displayed by the display according to the third embodiment of thepresent invention when an observer observes it from the normaldirection. FIG. 38 is a perspective view schematically showing anexample of the image displayed by the display shown in FIG. 37 when anobserver observes it from an oblique direction.

The display 1 shown in FIGS. 37 and 38 is the same as the display 1described with reference to FIGS. 1 and 2 except that the followingconfiguration is adopted. That is, the display 1 does not contain theregion 18, and the region 17 is provided with the print layer 14described with reference to FIGS. 32 to 34. The print layer 14 is formedof functional ink whose color changes in accordance with the observationdirection.

When the display 1 is observed from the normal direction, the regions 13and 17 typically display, as shown in FIG. 37, different colors. Then,if the observation direction is sufficiently inclined, as shown in FIG.38, both of the regions 13 and 17 change the display colors.

The print layer 14 may be arranged to face opposite a portion of therelief structure RS1. This will be described with reference to FIGS. 39to 41.

FIG. 39 is a plan view schematically showing a modification of thedisplay shown in FIG. 33. FIG. 40 is a sectional view taken along anXXXIII-XXXIII line of the display shown in FIG. 39. FIG. 41 is aperspective view schematically showing an example of the image displayedby the display shown in FIGS. 39 and 40 when an observer observes itfrom the oblique direction.

The display 1 shown in FIGS. 39 and 40 is the same as the display 1described with reference to FIG. 33 except that the followingconfiguration is adopted. That is, the display 1 does not contain theregion 18. The relief structure RS1 is provided not only in the region13, but also in the region 17. Then, the print layer 14 is provided notonly in the region 17, but also in the region 13.

The relief structure RS1 provided in the region 13 and the reliefstructure RS1 provided in the region 17 have, for example, the samestructure. Different relief structures RS1 may be provided on thesurface of the relief structure formation layer 112. In such a case, theboundary of such relief structures RS1 may match the boundary of theregions 13 and 17 or may be different from the boundary of the regions13 and 17. It is assumed here that, as an example, the same reliefstructure RS1 is provided in the regions 13 and 17.

The print layer 14 is provided in a stripe shape. A portion of the printlayer 14 positioned in the region 13 is formed of a plurality of stripportions each extending in the Y direction and arranged in the Xdirection. A portion of the print layer 14 positioned in the region 17is formed of a plurality of strip portions each extending in the Xdirection and arranged in the Y direction. In each of the regions 13 and17, the strip portions are arranged at a density of, for example, 3 to10 strip portions per millimeter. The density of the strip portions isthe same in the regions 13 and 17.

As described above, the strip portions are arranged at a density of 3 to10 strip portions per millimeter in the regions 13 and, 17. Thus, whenobserved with the naked eye, it is impossible or difficult todiscriminate each strip portion from other strip portions. Further, asdescribed above, the relief structure RS1 has the same structure in theregions 13 and 17, and the density of strip portion is the same in bothregions. Thus, when the display 1 is observed from the normal direction,as shown in FIG. 39, it is impossible or difficult to discriminate theregions 13 and 17 from each other.

When the observation direction is inclined in a plane perpendicular tothe X direction or the Y direction, the apparent density of the stripportions increases in one of the regions 13 and 17. Thus, a portion ofthe print layer 14 positioned in the region 13 and a portion of theprint layer 14 positioned in the region 17 affect the displaydifferently. For example, when the observation direction is inclined ina plane perpendicular to the X direction as shown in FIG. 41, the region17 is seen darker than the region 13. Further, as described above, ifthe observation direction is inclined, the hue of the color displayed bythe relief structure RS1 also changes. Therefore, if the observationdirection is inclined in, for example, a plane perpendicular to the Xdirection, a latent image formed by the regions 13 and 17 is visualizedby being accompanied by the change in hue.

Therefore, if the configuration described with reference to FIGS. 39 to41 is adopted, a more complex visual effect can be achieved.

In the example described with reference to FIGS. 39 to 41, the printlayer 14 is formed of two portions in which the length directions ofstrip portions are different and the relief structure RS1 is provided toface these portions. The relief structure RS1 may be provided to faceonly one of these portions or face a portion of one portion and at leasta portion of the other portion.

Alternatively, the relief structure S1 may not face the print layer 14.For example, the relief structure RS1 and the print layer 14 may bearranged so that the region where the relief structure RS1 is providedand the region where the print layer 14 is provided are adjacent to eachother when observed from the normal direction. When the observationdirection is inclined, the display 1 adopting the above structure causesthe change in hue in the region where the relief structure RS1 isprovided and visualizes a latent image in the region where the printlayer 14 is provided.

Fourth Embodiment

Next, the fourth embodiment of the present invention will be described.

A display according to the fourth embodiment is the same as the display1 according to the first or second embodiment except that a structuredescribed below is adopted in a region 13. That is, in the presentembodiment, a reflection surface 22 has a shape extending in onedirection.

FIG. 42 is a perspective view schematically showing an example of thestructure that can be adopted for a display according to the fourthembodiment of the present invention.

In a relief structure RS1 shown in FIG. 42, the reflection surfaces 22have shapes extending in the X direction and are arranged in the Ydirection. The center-to-center distances of the reflection surfaces 22adjacent in the width direction are irregular and the widths of thereflection surfaces 22 are also irregular. The center-to-centerdistances of the reflection surfaces 22 adjacent in the width directionmay be regular. Alternatively, the widths of the reflection surfaces 22may be regular.

When observed from a direction perpendicular to the X direction, therelief structure RS1 displays a mixed color. Then, observed from adirection perpendicular to the Y direction, the relief structure RS1displays an achromatic color, for example, silver gray.

Thus, if the relief structure RS1 shown in FIG. 42 is observed from anoblique direction while rotating the relief structure RS1 around thenormal of a reflection surface 21, the display color changes betweenchromatic colors and achromatic colors. Then, different from a generaldiffraction grating, if the relief structure RS1 shown in FIG. 42 isobserved from a direction perpendicular to an axis parallel to thelength direction of the reflection surface 22 while swinging the reliefstructure RS1 around the axis, the display color does not changesignificantly.

Such a visual effect cannot be achieved by general printed matter, norcan be achieved by a diffraction grating or hologram, nor can beachieved by a combination of a light-scattering structure and apigmented layer. That is, the relief structure RS1 provides an extremelyspecial visual effect.

The relief structure RS1 shown in FIG. 42 scatters light only indirections perpendicular to the X direction. Thus, compared with arelief structure that scatters light in all directions, the reliefstructure RS1 can make a bright display.

Moreover, as compared with a relief structure in which the reflectionsurface 22 is arranged two-dimensionally, the relief structure RS1 has asimple structure. Thus, the relief structure RS1 shown in FIG. 42 iseasy to design and produce.

The relief structure RS1 shown in FIG. 42 can be modified in variousways.

FIG. 43 is a plan view schematically showing an example of amodification of the relief structure shown in FIG. 42. FIG. 44 is a planview schematically showing another example of the modification of therelief structure shown in FIG. 42.

In the relief structures RS1 shown in FIGS. 43 and 44, the reflectionsurfaces 22 have shapes extending in the X direction and are arranged inthe X and Y directions. The center-to-center distances of the reflectionsurfaces 22 adjacent in the width direction are irregular and the widthsof the reflection surfaces 22 are also irregular. The distances betweenthe reflection surfaces 22 adjacent in the length direction areirregular and the lengths of the reflection surfaces 22 are alsoirregular.

The relief structure RS1 described above can scatter light also in adirection perpendicular to the Y direction, though not so intensive asin a direction perpendicular to the X direction. Therefore, if the ratioof the length to the width of the reflection surface 22 is 10 or less,the relief structure RS1 may also display a mixed color when observedfrom a direction perpendicular to the Y direction.

If the ratio of the length to the width of the reflection surface 22 issmall, the relief structure RS1 may display the same mixed color whenobserved from a direction perpendicular to the Y direction and whenobserved from a direction perpendicular to the X direction. When theratio is, for example, 10 or more, an observer can perceive thedifference between a mixed color displayed by the relief structure RS1when observed from a direction perpendicular to the X direction and amixed color displayed by the relief structure RS1 when observed from adirection perpendicular to the Y direction.

In the present embodiment, the reflection surface 22 can have variousshapes. For example, the reflection surface 22 may be square as shown inFIG. 43 or rounded as shown in FIG. 44. An intermediate portion of thecontour of the reflection surface 22 that is sandwiched between two endsmay be linear as shown in FIGS. 43 and 44 or curved. When the contour ofthe reflection surface 22 is curved in the intermediate portion, therelief structure RS1 can scatter light also in a direction perpendicularto the Y direction.

The length direction of the reflection surface 22 may be directionintersecting the X direction. For example, the length direction of thereflection surface 22 may be parallel to the Y direction.

FIG. 45 is a plan view schematically showing an example of the displayincluding the relief structure shown in FIG. 42. FIG. 46 is aperspective view schematically showing an example of the image displayedby the display shown in FIG. 45. FIG. 47 is a perspective viewschematically showing another example of the image displayed by thedisplay shown in FIG. 45.

The display 1 shown in FIG. 45 is the same as the display 1 describedwith reference to FIGS. 1 and 2 except that the following configurationis adopted. That is, the display 1 does not contain a region 17, and therelief structure RS1 provided in the region 13 has the structuredescribed with reference to FIG. 42.

In the region 13 of the letter “T”, the reflection surfaces 22 have thelength directions parallel to the X direction and are arranged in the Ydirection. Here, as an example, the average center-to-center distance ofthe reflection surfaces 22 is about 1 μm and the difference betweenheights of the reflection surfaces 21 and 22 is about 0.3 μm in theregion 13.

In the region 13 of the letter “O”, the reflection surfaces 22 have thelength directions parallel to the Y direction and are arranged in the Xdirection. Here, as an example, the average center-to-center distance ofthe reflection surfaces 22 is about 1 μm and the difference betweenheights of the reflection surfaces 21 and 22 is about 0.25 μm in theregion 13.

In the region 13 of the letter “P”, the reflection surfaces 22 have thelength directions parallel to the X direction and are arranged in the Ydirection. Here, as an example, the average center-to-center distance ofthe reflection surfaces 22 is about 1 μm and the difference betweenheights of the reflection surfaces 21 and 22 is about 0.2 μm in theregion 13.

When observed from an oblique direction perpendicular to the X directionas shown in FIG. 46, the display 1 displays yellow at the region 13 ofthe letter “T”, an achromatic color at the region 13 of the letter “O”,and purple at the region 13 of the letter “P”. In this case, when theangle of incidence of illumination light is increased, the colordisplayed at the region 13 of the letter “T” and the region 13 of theletter “P” by the display 1 changes to blue-green and orange,respectively.

When observed from an oblique direction perpendicular to the Y directionas shown in FIG. 47, the display 1 displays an achromatic color at theregion 13 of the letter “T”, blue at the region 13 of the letter “O”,and an achromatic color at the region 13 of the letter “P”. In thiscase, when the angle of incidence of illumination light is increased,the color displayed at the region 13 of the letter “O” by the display 1changes to purple.

As described above, the relief structure RS1 described with reference toFIGS. 42 to 44 can provide complex visual effects.

Techniques described in the first to fourth embodiments can mutually becombined. For example, the display 1 may contain two or more structuresdescribed in the first to fourth embodiments. The display 1 according tothe first, third, and fourth embodiments may contain a plurality ofpixels PX. In such a case, the structure described in the secondembodiment may be adopted for these pixels. The display according to thefirst, second, and fourth embodiments may further contain the printlayer 14 described in the third embodiment.

The display 1 described above can be used as a forgery-prevention labelwhen supported by, for example, printed matter. As described above, thedisplay 1 provides a special visual effect. The display 1 is difficultto forge. Therefore, it is difficult to forge or imitate a labeledarticle including an article and the display 1 supported thereby.

FIG. 48 is a plan view schematically showing an example of a labeledarticle. FIG. 49 is a sectional view taken along an IL-IL line of thelabeled article shown in FIG. 48.

FIGS. 48 and 49 depict printed matter 100 as an example of the labeledarticle. The printed matter 100 is an integrated circuit (IC) card andcontains a substrate 50. The substrate 50 is made of, for example,plastics. The substrate 50 has a recess provided on one main surface,and an IC chip 30 is embedded in the recess. Electrodes are provided onthe surface of the IC chip 30, and information is written into the IC orinformation recorded in the IC is read via these electrodes. A printlayer 40 is formed on the substrate 50. The above display 1 is fixedvia, for example, an sticky layer to the surface of the substrate 50 onwhich the print layer 40 is formed. The display 1 is prepared, forexample, as a self-adhesive sticker or transfer foil and fixed to thesubstrate 50 by being pasted to the print layer 40.

The printed matter 100 includes the display 1. Therefore, it isdifficult to forge or imitate the printed matter 100. Moreover, theprinted matter 100 includes, in addition to the display 1, the IC chip30 and the print layer 40 and therefore, forgery-prevention measuresusing the IC chip 30 or the print layer 40 can further be adopted.

Although FIGS. 48 and 49 illustrate an IC card as printed matterincluding the display 1, the printed matter including the display 1 isnot limited to the above example. For example, printed matter includingthe display 1 may be a different card such as a magnetic card, wirelesscard, and identification (ID) card. Alternatively, printed matterincluding the display 1 may be securities such as vouchers and checks.Alternatively, printed matter including the display 1 may be a tag to beattached to an article whose authenticity as an authentic article shouldbe verified. Alternatively, printed matter including the display 1 maybe a package or a portion thereof that accommodates an article whoseauthenticity as an authentic article should be verified.

Although the display 1 is pasted to the substrate 50 in the printedmatter 100 shown in FIGS. 48 and 49, the substrate can be caused tosupport the display 1 by other methods. For example, when paper is usedas the substrate, it is possible that the paper is made to embed thedisplay 1 and the paper is opened at the position corresponding to thedisplay 1. Alternatively, when a light-transmitting material is used asthe substrate, the display may be embedded in the material or thedisplay 1 may be fixed to the back side of the substrate, that is, tothe surface on the opposite side of the display surface.

A labeled article may not be printed matter. That is, an article thatdoes not contain a print layer may be caused to support the display 1.For example, an article of quality, for example, an art object may becaused to support the display 1.

The display 1 may be used for other purposes than forgery prevention.For example, the display 1 may be used as a toy, learning material, orornament.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

What is claimed is:
 1. A display comprising: one or more first reliefstructures, wherein each of the one or more first relief structuresconsists of a smooth first reflection surface and a plurality ofprotrusions or recesses, each top surface of the protrusions or eachbottom of the recesses is a smooth second reflection surface parallel tothe first reflection surface, each of the one or more first reliefstructures is configured to display a color as a structural color byemitting a plurality of wavelength components of visible lightwavelengths in the same direction, each of the second reflectionsurfaces has a height or depth relative to the first reflection surfacein a range of 0.1 to 0.5 μm, and in each of the one or more first reliefstructures, the second reflection surfaces all have the same shape anddimensions as each other, and are arranged at a regular center-to-centerdistance along a first direction and at a regular center-to-centerdistance along a second direction substantially perpendicular to thefirst direction, each of the second reflection surfaces has a length anda width in a range of 5 to 10 μm, and a ratio S1/S of an area S1 of anorthogonal projection of the first reflection surface on a planeparallel to the first reflection surface to an area S of an orthogonalprojection of the first relief structure on the plane is in a range of20 to 80%.
 2. The display according to claim 1, wherein in at least oneof the one or more first relief structures, the second reflectionsurfaces are arranged regularly at average intervals in a range of 5 to50 μm, and a radio S2/S of an area S2 of an orthogonal projection of thesecond reflection surfaces on a plane parallel to the first reflectionsurface to an area S of an orthogonal projection of the first reliefstructure on the plane is in a range of 20 to 80%.
 3. The displayaccording to claim 2, wherein in at least one of the one or more firstrelief structures, the second reflection surfaces are arranged regularlyand have an equal height or depth relative to the first reflectionsurface.
 4. The display according to claim 1, wherein a number of theone or more first relief structures is two or more, one of the firstrelief structures and another of the first relief structures areconfigured to display different colors, the second reflection surfaceshave an equal height or depth relative to the first reflection surfacein each of the first relief structures displaying the different colors,and one of the first relief structures displaying the different colorsand another of the first relief structures displaying the differentcolors are different from each other in the heights or depths of thesecond reflection surfaces relative to the first reflection surface. 5.The display according to claim 1, further including a print layer. 6.The display according to claim 5, wherein the print layer and at leastone of the one or more first relief structures display a latent imagewhen observed in a normal direction and display a visible image whenobserved in an oblique direction.
 7. The display according to of claim1, further including one or more second relief structures, wherein eachof the one or more second relief structures constitutes one of adiffraction grating, a hologram, a light-absorbing structure thatdisplays a color between dark gray and black when illuminated with whitelight, and a light-scattering structure that emits white light asscattered light when illuminated with white light.
 8. The displayaccording to claim 1, including a plurality of pixels arrangedtwo-dimensionally, wherein each of the first relief structuresconstitutes a portion or a whole of one of the pixels.
 9. The displayaccording to claim 8, wherein the plurality of pixels include two ormore pixels having an equal area ratio and two or more pixels havingdifferent area ratios, the area ratio being a ratio of an area of thefirst relief structure to an area of the pixel, and the two or morepixels having an equal ratio are equal to each other in heights ordepths of the second reflection surfaces relative to the firstreflection surface, and the two or more pixels having different arearatios are different from each other in heights or depths of the secondreflection surfaces relative to the first reflection surface.
 10. Thedisplay according to claim 9, wherein in the two or more pixels havingdifferent area ratios, the heights or depths of the second reflectionsurfaces relative to the first reflection surface are greater in thepixel having the larger area ratio than in the pixel having the smallerarea ratio.
 11. The display according to claim 9, wherein three or moreof the pixels are arranged in an order of the ratio.
 12. The displayaccording to claim 1, comprising: a relief structure formation layer;and a reflection layer at least partially covering one main surface ofthe relief structure formation layer, the first relief structures beingprovided at an interface between the relief structure formation layerand the reflection layer or on a surface of the reflection layer. 13.The display according to claim 1, wherein each of the one or more firstrelief structures, the width of each of the second reflection surfacesis substantially the same as the length of each of the second reflectionsurfaces.
 14. A labeled article comprising: the display according toclaim 1; and an article supporting the display.
 15. A displaycomprising: one or more first relief structures, wherein each of the oneor more first relief structures consists of a smooth first reflectionsurface and a plurality of protrusions or recesses, each top surface ofthe protrusions or each bottom of the recesses is a smooth secondreflection surface parallel to the first reflection surface, and in eachof the one or more first relief structures, the second reflectionsurfaces all have the same shape and dimensions as each other, and arearranged at a regular center-to-center distance along a first directionand at a regular center-to-center distance along a second directionsubstantially perpendicular to the first direction.
 16. The displayaccording to claim 15, wherein each of the one or more first reliefstructures is configured to display a color as a structural color byemitting a plurality of wavelength components of visible lightwavelengths in the same direction.
 17. The display according to claim15, wherein each of the second reflection surfaces has a height or depthrelative to the first reflection surface in a range of 0.1 to 0.5 μm.18. The display according to claim 15, wherein in each of the one ormore first relief structures, each of the second reflection surfaces hasa length and a width in a range of 5 to 10 μm.
 19. The display accordingto claim 15, wherein in each of the one or more first relief structures,a ratio S1/S of an area S1 of an orthogonal projection of the firstreflection surface on a plane parallel to the first reflection surfaceto an area S of an orthogonal projection of the first relief structureon the plane is in a range of 20 to 80%.
 20. A labeled articlecomprising: the display according to claim 15; and an article supportingthe display.